1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method that can correct a color of an image to be output from a printer, and a program that can generate image processing parameters.
2. Description of the Related Art
The recent improvement in performance of electrophotographic apparatuses can realize high image quality comparable to that of a printing machine. However, the instability of each electrophotographic apparatus tends to cause a color variation that is larger than that of a printing machine.
In general, a “single-color” calibration technique is conventionally available for an electrophotographic apparatus. The “single-color” calibration technique includes generating a look-up table (LUT) usable to correct one-dimensional gradation characteristics corresponding to each of cyan, magenta, yellow, and black (hereinafter, simply referred to as C, M, Y, and K) toners. The LUT is a table that indicates output data corresponding to respective input data segmented at specific intervals. Using the LUT is useful in expressing nonlinear characteristics to which no calculation formula is available. Further, the “single-color” is a color that is producible using a single toner of C, M, Y, or K. Performing the single-color calibration is useful to correct single-color reproduction characteristics (e.g., maximum density and gradation).
Further, as discussed in Japanese Patent Application Laid-Open No. 2011-254350, a “multi-color” calibration technique using a four-dimensional LUT is conventionally proposed. The “multi-color” is a composite color that is reproducible using a plurality of toners of red, green, and blue or gray (based on CMY). Especially, according to electrophotography, even when a one-dimensional LUT is used to correct single-color gradation characteristics, a nonlinear difference tends to occur if a plurality of toners is used to express a “multi-color.” Performing the multi-color calibration is useful to correct multi-color reproduction characteristics, which can be expressed by a combination (e.g., a superposition) of a plurality of color toners.
A processing procedure including a “multi-color” calibration is described below. The processing includes printing patches on a recording medium (e.g., a paper) based on single-color chart data that is usable to perform the “single-color” calibration and reading the printed patches with a scanner or a sensor. The processing further includes comparing read patch data with target values having been set beforehand and generating a one-dimensional LUT usable to correct differences between read patch data and the target values. The processing further includes printing patches on a recording medium based on multi-color chart data that reflects the obtained one-dimensional LUT to perform the “multi-color” calibration and reading the printed patches with the scanner or the sensor. The processing includes comparing the read patch data with target values having been set beforehand and generating a four-dimensional LUT usable to correct differences between read patch data and the target values.
As mentioned above, it is conventionally feasible to realize highly accurate correction by performing the “multi-color” calibration in such a way as to correct multi-color characteristics that cannot be corrected by the “single-color” calibration.
However, according to the above-mentioned technique, the multi-color calibration can be started on condition that gradation characteristics have been already corrected in the single-color calibration. In other words, it is required to complete the single-color calibration before starting the multi-color calibration. Therefore, a long processing time is required to accomplish the multi-color calibration.
For example, if it is determined that an image obtained after the multi-color calibration is insufficient in image quality, it is difficult to identify a failure having occurred in the single-color calibration or the multi-color calibration. Accordingly, it is necessary to re-execute the single-color calibration and the multi-color calibration in this order. The working time for the entire calibration processing greatly increases.
On the other hand, constantly restarting the multi-color calibration while skipping the single-color calibration may be useful to reduce the processing time. However, in a case where the single-color calibration has not been successfully completed, the correction accuracy will deteriorate significantly in the multi-color calibration to be performed subsequently.
From the reason described above, the multi-color calibration may not be easy to use for a user in a specific situation.